1. Field of the Invention
The present invention relates to a display apparatus used as a display incorporated in a cellular phone, an electronic book and the like. More specifically, the present invention relates to an active matrix type display apparatus incorporating a digital memory cell in a pixel, and to a method of driving the same.
2. Description of the Related Art
Liquid crystal display apparatus has been used as a display of a portable information terminal while utilizing advantages of a light weight, a thin thickness and low power consumption. Since such a portable information terminal generally adopts a battery-driven type, low power consumption is an important subject for it. Particularly, cellular telephones are required to be capable of displaying with low power consumption during a standby period.
As a technology to realize the displaying with the low power consumption, disclosed are active matrix type liquid crystal display apparatuses incorporating digital memory cells (DM cells) (hereinafter referred to as a liquid crystal display apparatus incorporating DM cells) as a storage device which is capable of storing video data statically in one pixel. There is U.S. Pat. No. 5,712,652 as a document disclosing such a kind of liquid crystal display apparatus incorporating DM cells. In the image display apparatus disclosed in this gazette, only circuits for AC-driving the liquid crystal by binary data stored in the DM cells are operated during a standby period (still image displaying period), and peripheral driving circuits other than these circuits are stopped to operate, whereby power consumption can be significantly decreased.
Incidentally, in the conventional liquid crystal display apparatuses incorporating DM cells, SRAMs are used as the DM cells. Each of these SRAMs is usually constituted by five transistors. Therefore, to dispose the DM cells on a substrate, an area having a size to some extent is required, and hence microfabrication of the liquid crystal display apparatus is difficult.
An object of the invention is to realize a microfabrication of a pixel in a display apparatus incorporating DM cells.
A display apparatus according to the present invention including a first electrode substrate having a plurality of scan lines and a plurality of signal lines arranged so as to intersect with each other, pixel electrodes, each being arranged at corresponding one of crossing points of the scanning and signal lines, first capacitor elements, each being electrically in parallel connected to corresponding one of the pixel electrodes, and first switching elements, each being turned ON/OFF by a row selection signal supplied to the corresponding one of the scan lines, and when turned ON, allowing the signal line and the pixel electrode to be electrically conducted, thus writing video data supplied to the signal line to the pixel electrode, a second electrode substrate having opposite electrodes, oppositely disposed so as to face the said pixel electrodes with a predetermined gap therebetween, a display layer sandwiched between the first and second electrode substrates, a data driver for supplying the video data to the plurality of signal lines in response to one horizontal scanning period and a scan driver circuit for sequentially supplying the row selection signal to the corresponding one of the scan lines every the one horizontal scanning period, wherein the first electrode substrate has, a digital memory cell composed of one inverter circuit capable of retaining the video data supplied to the signal line, and a digital memory switching circuit for controlling an electrical conduction between the pixel electrode and the digital memory cell.
A method of driving the display apparatus has features in that during a first displaying period, the pixel electrode and the digital memory cell are not electrically conducted by the digital memory switching circuit, and the first switching element is turned on at a predetermined cycle, thus performing displaying by writing first video data supplied to the signal line to the pixel electrode, and during a second displaying period, the pixel electrode and the digital memory cell are electrically conducted by the digital memory switching circuit, the digital memory cell is allowed to retain second video data therein supplied to the signal lines, and then the signal lines and the pixel electrode are not electrically conducted by the first switching element, thus performing displaying by writing the second video data retained in the digital memory cell to the pixel electrode.